Cobalt powder production method

ABSTRACT

Provided is a production method for producing coarse particles of high purity Co powder from a cobalt ammine sulfate complex solution using fine Co powder and using industrially inexpensive H 2  gas.

BACKGROUND Field of the Invention

The present invention relates to a method for obtaining high purity cobalt powder from a cobalt ammine sulfate complex solution and briquettes prepared by shaping the powder.

Description of the Related Art

A method for industrially producing cobalt powder using a hydrometallurgical process includes a method for producing cobalt powder by dissolving a raw material in a sulfuric acid solution followed by removing impurities to obtain a cobalt sulfate solution, adding ammonia to the resulting cobalt sulfate solution to form an ammine complex of cobalt, and feeding hydrogen gas into the produced cobalt ammine sulfate complex solution to reduce cobalt.

For example, Japanese Translation of PCT International Application Publication No. JP-T-08-503999 describes a process for producing cobalt powder by adding silver as seed crystals during the reduction reaction to precipitate cobalt on the seed crystals.

Specifically, the process is a method of producing cobalt powder from an ammoniacal cobalt sulfate solution, including: adding silver sulfate or silver nitrate to the solution in an amount such that the proportion of soluble silver to cobalt is about 0.3 g to 10 g of silver per kg of cobalt to be reduced, adding an organic dispersant in an amount effective for preventing the aggregation of cobalt metal powder to be produced, and heating the resulting solution at a temperature in a range of 150 to 250° C. with stirring at a hydrogen pressure of 2500 to 5000 KPa for a time sufficient to reduce cobalt sulfate to cobalt metal powder.

However, the method has had a problem that affects product quality because the incorporation of silver derived from seed crystals into the product cannot be avoided.

There is also a method of obtaining cobalt powder using a reducing agent other than hydrogen gas.

For example, Japanese Patent Laid-Open No. 2010-242143 discloses cobalt powder suitable as conductive particles for conductive paste and multilayer capacitors, and a method for producing the same. The method provides a method for producing metal powder by a liquid phase reduction method that is improved so that a particle aggregate may be hardly produced. Specifically, the method for producing metal powder includes a first step of dissolving a metal compound, a reducing agent, a complexing agent, and a dispersant to prepare an aqueous solution containing metal ions derived from the metal compound and a second step of adjusting the pH of the aqueous solution to reduce the metal ions with the reducing agent to precipitate the metal powder.

However, this production method requires high cost since a large amount of expensive chemicals is used, and has had economically disadvantageous problem for applying the method to the industrial cobalt smelting process as described above.

Further, Translation of PCT International Application Publication No. JP-T-2006-516679 discloses a method for recovering nickel and cobalt using ammonia.

This method is a method for the recovery of nickel and cobalt from nickel and cobalt-containing laterite ores, including: a) roasting feed ore in a reducing atmosphere in a rotary kiln to selectively reduce the nickel and cobalt, wherein either no, or less than 2.5% by weight of reducing agent is added to the feed ore prior to roasting; b) leaching the reduced ore with an aerated solution of ammoniacal ammonium carbonate to extract the nickel and cobalt into a leach solution; and c) separating the ore tailings from the leach solution and recovering the nickel and cobalt by a process selected from ammoniacal solvent extraction, precipitation techniques or ion exchange.

Further, Japanese Patent Laid-Open No. 06-116662 discloses a method for recovering copper, nickel, and cobalt from an ammonia solution using hydrogen.

This method provides a method of efficiently leaching copper, nickel, and cobalt from a deep-sea oxide mineral using hydrogen. Specifically, activated hydrogen is provided to deep-sea oxide mineral particles dispersed in an ammonia-ammonium salt solution in the presence of a hydrogen-reducible reaction medium; the reaction medium is reduced by the activated hydrogen; and the above deep-sea oxide mineral is reduced by the reaction medium to thereby leach copper, nickel, and cobalt in the mineral as ammine complex ions.

However, this method requires a catalyst in which noble metal such as platinum is carried on the surface of an inert solid in order to accelerate the reduction reaction, and the method cannot be said to be advantageous considering the cost required for the amount of the catalyst and the replenishment for the natural decrease of the catalyst required when performed on an industrial scale.

Although various processes for producing cobalt powder have been proposed as described above, there has been no method for producing high purity cobalt powder using industrially inexpensive hydrogen gas.

In such a situation, the present invention intends to provide a production method for producing coarse particles of high purity cobalt powder from a cobalt ammine sulfate complex solution using fine cobalt powder and using industrially inexpensive hydrogen gas.

SUMMARY

A first aspect of the present invention to solve such a problem is a method for producing cobalt powder, including the following steps (1) to (4) of: (1) a seed crystal addition step of adding cobalt powder as seed crystals to a cobalt ammine sulfate complex solution to form a mixed slurry; (2) a reduction step of blowing hydrogen gas into the mixed slurry obtained in the seed crystal addition step to precipitate a cobalt component in the mixed slurry onto the seed crystals by hydrogen reduction reaction to form cobalt powder, and thereby to form a reduced slurry containing the cobalt powder; (3) a growth step of adding the cobalt ammine sulfate complex solution to the cobalt powder obtained by solid-liquid separation of the reduced slurry formed in the reduction step to form a slurry, blowing hydrogen gas into the resulting slurry, and reducing, precipitating, and growing a cobalt component in the slurry on the surface of the cobalt powder by hydrogen reduction reaction to form a grown cobalt powder, and thereby to form a slurry containing the grown cobalt powder; and (4) a recovery step after the reduction step of subjecting the reduced slurry containing the cobalt powder obtained in the reduction step (2) to solid-liquid separation to separate and recover the cobalt powder as a solid phase component, and another recovery step after the growth step of subjecting the slurry containing the cobalt powder obtained in the growth step (3) to solid-liquid separation to separate and recover the cobalt powder as a solid phase component.

A second aspect of the present invention is a method for producing cobalt powder according to the first aspect, wherein, in the seed crystal addition step (1), a dispersant is further added to the mixed slurry when the seed crystals are added to the cobalt ammine sulfate complex solution to form a mixed slurry.

A third aspect of the present invention is a method for producing cobalt powder according to the first and second aspects, wherein, in the seed crystal addition step (1), the amount of the seed crystals added is 1 to 200% by weight with respect to the weight of cobalt in the cobalt ammine sulfate complex solution.

A fourth aspect of the present invention is a method for producing cobalt powder according to the first to third aspects, wherein the cobalt ammine sulfate complex solution is obtained by: a leaching step of dissolving the cobalt-containing material containing nickel and impurities; a nickel separation step of adjusting a pH of the leachate containing cobalt, nickel, and impurities and obtained in the leaching step and then separating the leachate into a crude cobalt sulfate solution and a nickel recovery solution by solvent extraction; a solution purification step of removing the impurities from the crude cobalt sulfate solution obtained in the nickel separation step by any or a combination of solvent extraction, a sulfurization method, and a neutralization method to obtain a cobalt sulfate solution; and a complexing step of subjecting the cobalt sulfate solution to complexing treatment with ammonia.

A fifth aspect of the present invention is a method for producing cobalt powder according to the fourth aspect, wherein the cobalt-containing material is at least one of cobalt and nickel mixed sulfide, crude cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt carbonate, and metallic cobalt powder.

A sixth aspect of the present invention is a method for producing cobalt powder according to the fourth and fifth aspects, wherein a solvent used in the solvent extraction of the nickel separation step and the solution purification step is 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester or di-(2,4,4-trimethylpentyl)phosphinic acid.

A seventh aspect of the present invention is a method for producing cobalt powder according to the first to third aspects, wherein, in the seed crystal addition step (1), the concentration of ammonium sulfate in the cobalt ammine sulfate complex solution is 100 to 500 g/l, and the ammonium concentration is 1.9 or more by mole with respect to the concentration of cobalt in the complex solution.

An eighth aspect of the present invention is a method for producing cobalt powder according to the first aspect, wherein, regarding the hydrogen reduction in the hydrogen reduction reactions in the reduction step (2) and the growth step (3), hydrogen reduction is performed by maintaining the temperature of 120 to 250° C. and the pressure of 1.0 to 4.0 MPa.

A ninth aspect of the present invention is a method for producing cobalt powder according to the second aspect, wherein the dispersant includes one or more of an acrylate and a sulfonate.

A tenth aspect of the present invention is a method for producing cobalt powder according to the first aspect, including: a cobalt powder briquetting step of processing the high purity cobalt powder obtained in the growth step (3) into cobalt briquettes in a block form using a briquetting machine; and a briquette sintering step of sintering the resulting cobalt briquettes in the block form under the condition of maintaining the temperature of 500 to 1200° C. in a hydrogen atmosphere to form cobalt briquettes as a sintered compact.

An eleventh aspect of the present invention is a method for producing cobalt powder according to the first aspect, including an ammonium sulfate recovery step of concentrating a solution after reaction obtained by separating cobalt powder as a solid phase component by the solid-liquid separation in the recovery steps (4) after the reduction step (2) and the growth step (3), to precipitate ammonium sulfate to recover ammonium sulfate crystals.

A twelfth aspect of the present invention is a method for producing cobalt powder according to the first aspect, including an ammonia recovery step of adding an alkali to a solution after reaction obtained by separating cobalt powder as the solid phase component by the solid-liquid separation in the recovery steps (4) after the reduction step (2) and the growth step (3), and heating the resulting mixture to volatilize and recover ammonia gas.

A thirteenth aspect of the present invention is a method for producing cobalt powder according to the first aspect, wherein the ammonia recovered in the ammonia recovery step is recycled in the production processes in the method for producing the cobalt powder according to the first aspect, and used as an alkali for pH adjustment in the nickel separation step according to the fourth aspect, as an alkali for neutralization when the neutralization method is used in the solution purification step according to the fourth aspect, and as an alkali used in the complexing step according to the fourth aspect.

A fourteenth aspect of the present invention is a method for producing cobalt powder according to the first aspect, wherein the seed crystals of the cobalt powder in the seed crystal addition step (1) is cobalt powder formed by adding a reducing agent to the cobalt sulfate solution obtained in the solution purification step according to the fourth aspect.

A fifteenth aspect of the present invention is a method for producing cobalt powder according to the first aspect, wherein the seed crystals of the cobalt powder in the seed crystal addition step (1) is cobalt powder formed by hydrogen reduction reaction in which an insoluble solid is added to the cobalt ammine sulfate complex solution obtained in the complexing step according to the fourth aspect and hydrogen gas is blown into the resulting mixture at high temperature and high pressure.

A sixteenth aspect of the present invention is cobalt briquettes obtained using the methods of the first to fifteenth aspects.

In a method for producing cobalt powder using hydrogen gas from a cobalt ammine sulfate complex solution, high purity cobalt powder and cobalt briquettes can be efficiently obtained by employing the present invention, and an industrially remarkable effect can be thus achieved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a production flow chart of cobalt powder according to the present invention.

FIG. 2 is a view showing the change in the average particle size by the number of times of the growth step in Example 1.

DETAILED DESCRIPTION

According to the present invention, in the production method for obtaining cobalt powder from a cobalt ammine sulfate complex solution, it is characterized in that high purity cobalt powder containing a smaller amount of impurities is produced from the cobalt ammine sulfate complex solution by subjecting a process solution of the hydrometallurgical process to the steps (1) to (4) in sequence discussed below.

Hereinafter, the method for producing high purity cobalt powder according to the present invention will be described with reference to the production flow chart of high purity cobalt powder according to the present invention shown in FIG. 1.

[Leaching Step]

First, the leaching step is a step of dissolving a cobalt-containing material, serving as a starting material, such as an industrial intermediate including one or a mixture selected from cobalt and nickel mixed sulfide, crude cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt carbonate, and cobalt powder, with sulfuric acid to leach cobalt to produce a leachate, and can be performed by a known method disclosed in Japanese Patent Laid-Open No. 2005-350766 and the like.

[Nickel Separation Step]

Next, the pH of the leachate is adjusted, and the resulting leachate is subjected to the nickel separation step.

This nickel separation step is a step of bringing an organic phase into contact with a pH-adjusted leachate (aqueous phase), which is obtained in the leaching step and then subjected to pH adjustment, to exchange the components in each phase, thereby increasing the concentration of some components in the aqueous phase and reducing the concentration of other different components.

In the present invention, “2-ethylhexylphosphonic acid mono-2-ethylhexyl ester” or “di-(2,4,4-trimethylpentyl)phosphinic acid” is used as the organic phase to selectively extract cobalt in the leachate of the aqueous phase, and a crude cobalt sulfate solution is obtained by stripping using sulfuric acid.

Further, ammonia produced in an ammonia recovery step as described below may be used as the aqueous ammonia used for pH adjustment during this step.

[Solution Purification Step]

The solution purification step is a step of reducing impurities contained in the crude cobalt sulfate solution obtained in the nickel separation step, and the step is performed by any one or a combination of solvent extraction of selectively extracting impurity elements in the crude cobalt sulfate solution using “2-ethylhexylphosphonic acid mono-2-ethylhexyl ester” or “di-(2,4,4-trimethylpentyl)phosphinic acid” as the organic phase to obtain a high purity cobalt sulfate solution, a sulfurization method of adding a sulfurizing agent such as hydrogen sulfide gas, sodium sulfide, potassium sulfide, and sodium hydrogen sulfide to selectively precipitate and remove impurities, and a neutralization method of adding an alkali such as sodium hydroxide, calcium hydroxide, sodium carbonate, calcium carbonate, and magnesium hydroxide to selectively precipitate and remove impurities.

[Complexing Step]

The complexing step is a step of adding ammonia in the form of ammonia gas or aqueous ammonia to the high purity cobalt sulfate solution obtained in the solution purification step to subject the solution to complexing treatment to produce a cobalt ammine sulfate complex which is an ammine complex of cobalt, thus forming a cobalt ammine sulfate complex solution thereof.

The ammonia is added so that the ammonium concentration at this time may be 1.9 or more by mole based on the concentration of cobalt in the solution. If the concentration of the ammonia to be added is less than 1.9, cobalt will not form an ammine complex, but a precipitate of cobalt hydroxide will be produced.

Further, in order to adjust the concentration of ammonium sulfate, ammonium sulfate may be added in this step.

The concentration of ammonium sulfate at this time is preferably 100 to 500 g/L. If the concentration is more than 500 g/L, solubility will be exceeded to precipitate crystals to prevent operation. Further, it is difficult to achieve a concentration of less than 100 g/L in terms of the metal balance in the process.

Also, ammonia produced in the ammonia recovery step as described below may be used as the ammonia gas or aqueous ammonia used in this step.

[Steps of Producing Cobalt Powder from Cobalt Ammine Sulfate Complex Solution]

The steps of producing cobalt powder from the high purity cobalt ammine sulfate complex solution shown by the treatment steps in FIG. 1 will be described below.

(1) Seed Crystal Addition Step

This is the step of adding cobalt powder as seed crystals in the form of a cobalt powder slurry to the cobalt ammine sulfate complex solution to form a mixed slurry containing the seed crystals.

The weight of the seed crystals added at this time is preferably 1 to 200% by weight based on the weight of cobalt in the cobalt ammine sulfate complex solution. If the weight of the seed crystals is less than 1%, the reaction efficiency during the reduction in the next step will be significantly reduced, which is not preferred. Further, if the weight of the seed crystals exceeds 200%, the amount of the seed crystals used will be excessively large, which generates a problem in the handling of the seed crystals and is not economical because the production of the seed crystals requires much cost. Thus, such an amount of seed crystals used is not preferred.

The cobalt powder can be produced by mixing a reducing agent with the high purity cobalt sulfate solution obtained in the solvent extraction step.

The reducing agents which can be used here include, but are not limited to, hydrazine and sodium sulfite which are widely used industrially.

At this time, an alkali may also be mixed, and pH is preferably adjusted to 7 to 12 using sodium hydroxide.

Further, a reaction temperature is preferably 25 to 80° C. If the temperature is less than 25° C., reaction time will increase, and the industrial application of the long reaction time will not be realistic. On the other hand, if the temperature is higher than 80° C., the material of a reaction vessel will be limited to increase the cost of equipment. Further, the particle size of the cobalt powder produced can be reduced by adding a small amount of surfactant at this time.

As an another method of producing seed crystals, the seed crystals can be produced by blowing hydrogen gas into a cobalt ammine sulfate complex solution under the conditions of the reduction step to be described below. At this time, recovery efficiency can be improved by adding an insoluble solid, such as iron powder, alumina balls, and zirconia balls, and a dispersant to the cobalt ammine sulfate complex solution.

The dispersant may be added to the mixed slurry containing seed crystals at the same time. Since the seed crystals are dispersed by adding the dispersant, the reaction efficiency in the reduction step as the next step can be effectively improved.

The dispersants used here include, but are not limited to, those having one or more of an acrylate and a sulfonate, and polyacrylates and lignin sulfonates are preferred as those which can be industrially inexpensively obtained.

(2) Reduction Step

Hydrogen gas is blown into the mixed slurry obtained in the seed crystal addition step (1) and cobalt is precipitated from the solution onto the seed crystals by the hydrogen reduction reaction at high pressure.

At this time, reaction temperature is preferably 120 to 250° C. If the temperature is less than 120° C., reduction efficiency will be reduced, and even if the temperature exceeds 250° C., the reaction will not be accelerated, and the loss of thermal energy and the like will increase, which is not preferred.

Further, the pressure during the reaction is preferably 1.0 to 4.0 MPa. If the pressure is less than 1.0 MPa, reaction efficiency will be reduced, and even if the pressure exceeds 4.0 MPa, there will be no influence on the reaction, and the loss of hydrogen gas will increase.

In the liquid of the mixed slurry, magnesium ions, sodium ions, sulfate ions, and ammonium ions are mainly present as impurities, but since these impurities all remain in the solution, high purity cobalt powder can be produced.

(3) Growth Step

To the slurry obtained by adding the cobalt ammine sulfate complex solution obtained in the complexing step described above to the high purity cobalt powder, is fed hydrogen gas at high pressure according to the same method as the reduction step (2), to reduce and precipitate the cobalt component in the slurry onto the high purity cobalt powder by the hydrogen reduction reaction, thereby to form a slurry containing grown cobalt particles.

Further, high purity cobalt powder having a larger particle size can be produced by repeating this growth step a plurality of times. Further, the high purity cobalt powder having a larger particle size is separated into high purity cobalt powder and a solution after reaction by a recovery step. The resulting high purity cobalt powder may be finished into the shape of briquettes, which are coarser, more difficult to oxidize, and more easily handled, through the briquetting and briquette firing steps described below.

Furthermore, the ammonium sulfate contained in the solution after reaction obtained in the recovery step can be recovered in an ammonium sulfate recovery step, or ammonia can also be recovered in an ammonia recovery step.

(4) Recovery Steps after Reduction Step and Growth Step

The reduced slurry formed in the reduction step (2) or the slurry containing the grown cobalt particles formed in the growing step (3) is subjected to solid-liquid separation to recover high purity cobalt powder and a solution after reaction.

[Cobalt Powder Briquetting Step]

The high purity cobalt powder produced by the present invention is dried and then processed for shaping with a briquetting machine or the like to obtain cobalt briquettes in a block form as a product form.

Further, in order to improve the processability to form the briquettes, a material that does not impair the product quality such as water may be added as a binder to the cobalt powder depending on conditions.

[Briquette Sintering Step]

The cobalt briquettes prepared in the briquetting step is subjected to roasting and sintering in a hydrogen atmosphere to make a briquette sintered compact. This treatment is performed for increasing the strength and removing ammonia, sulfur, and carbon components remaining in a very small amount, and the roasting and a sintering temperature of the treatment is preferably 500 to 1200° C. If the temperature is less than 500° C., the sintering will be insufficient, and even if the temperature exceeds 1200° C., the efficiency will hardly change but the loss of energy will increase.

[Ammonium Sulfate Recovery Step]

Ammonium sulfate and ammonia are contained in the solution after reaction produced in the recovery step (4).

Thus, ammonium sulfate can be recovered as ammonium sulfate crystals by heating and concentrating the solution after reaction to crystallize ammonium sulfate.

[Ammonia Recovery Step]

On the other hand, an alkali is added to the solution after reaction to adjust the pH to a range of 10 to 13, and then the resulting solution can be heated to volatilize ammonia as a gas to recover the ammonia.

The alkali used here preferably includes, but is not limited to, sodium hydroxide and slaked lime, because they are industrially inexpensive.

Further, the recovered ammonia gas is brought into contact with water to produce aqueous ammonia, and the resulting aqueous ammonia may also be repeatedly used for the pH adjustment before the nickel separation step to which ammonia is added, in the solution purification step in the case of using the solvent extraction, and in the complexing step.

EXAMPLES

The present invention will be described below in more detail using Examples.

Example 1 (1) Seed Crystal Addition Step

To a solution containing cobalt sulfate in which 75 g of cobalt was contained and 330 g of ammonium sulfate, was added 191 ml of 25% aqueous ammonia to prepare a solution, which was adjusted so that the total volume of the solution was 1000 ml. To the resulting solution, were added 75 g (100% based on the weight of cobalt) of cobalt powder having an average particle size of 10 μm as seed crystals and 12.5 g of sodium polyacrylate (40% solution) as a dispersant to prepare a mixed slurry.

(2) Reduction Step

The mixed slurry prepared in the seed crystal addition step was charged to an autoclave and heated to 185° C. with stirring, and then hydrogen gas was blown and fed into the mixed slurry so that the pressure in the autoclave became 3.5 MPa to subject the mixed slurry to cobalt powder production treatment which is reduction treatment.

After the lapse of one hour from the start of feeding hydrogen gas, the feed of hydrogen gas was stopped, and the autoclave was cooled.

(3) Recovery Step after Reduction Step

A reduced slurry obtained after cooling was subjected to solid-liquid separation by filtration, and the slurry was separated to recover high purity cobalt powder having a small size and a solution after reaction. The cobalt powder recovered at this time was 141 g.

(4) Growth Step

Next, to a solution containing cobalt sulfate in which 75 g of cobalt is contained and 330 g of ammonium sulfate, was added 191 ml of 25% aqueous ammonia to prepare a solution, which was adjusted so that the total volume of the solution was 1000 ml.

To the resulting solution, was added the entire amount of the high purity cobalt powder having the small size obtained in the above recovery step after the reduction step as seed crystals to prepare a mixed slurry.

The mixed slurry was charged to an autoclave and heated to 185° C. with stirring, and hydrogen gas was blown and fed into the slurry so that the pressure in the autoclave became 3.5 MPa.

After the lapse of one hour from the start of feeding hydrogen gas, the feed of hydrogen gas was stopped, and the autoclave was cooled. A slurry obtained after cooling was subjected to solid-liquid separation by filtration to recover high purity cobalt powder having grown particles.

A portion of the cobalt powder was divided to measure the particle size using a known method, and the remainder was added as the cobalt powder having a small size described in the above growth step to repeat the growth step in which the cobalt powder having a small size is subjected to the reduction with hydrogen gas in the autoclave.

FIG. 2 shows the average particle size (μm) of cobalt powder versus the number of times of the growth step (which is the number of times of repetition) (times). It was verified that the cobalt powder grew and coarsened for every repetition.

The number of times of repetition may be optionally determined taking the productivity and the economical efficiency, such as required size of powder and required facility size and labor, into consideration.

Example 2

To 1000 ml of a cobalt ammine sulfate complex solution shown in Table 1, was added 75 g of cobalt powder having an average particle size of 10 μm as seed crystals. Then, the resulting mixture was charged to an autoclave and then heated to 185° C. with stirring, and hydrogen gas was blown and fed into the mixture so that the pressure in the autoclave became 3.5 MPa.

After the lapse of one hour from the start of feeding hydrogen gas, the feed of hydrogen gas was stopped, and the autoclave was cooled. A slurry obtained after cooling was subjected to solid-liquid separation by filtration to recover cobalt powder, which was washed with pure water and then analyzed for the impurity content in the cobalt powder.

The results are shown in Table 1.

The mixing of Mg, Na and Ca into the cobalt powder was not observed, and high purity cobalt powder was able to be produced.

TABLE 1 Co Mg Na Ca Cobalt ammine sulfate 31 0.9 31 0.2 complex solution [g/L] High purity cobalt powder — <0.005 <0.005 <0.005 [wt %]

Comparative Example 1

To a solution containing cobalt sulfate in which 75 g of cobalt is contained and 330 g of ammonium sulfate, was added 191 ml of 25% aqueous ammonia to prepare a solution, which was adjusted so that the total volume of the solution was 1000 ml.

The slurry was charged to an autoclave without adding seed crystals, and then hydrogen gas was fed until the pressure in the autoclave became 3.5 MPa, with stirring, followed by heating to 185° C. followed by holding the temperature for one hour. The amount of cobalt powder which was able to be recovered from the inside of the autoclave after cooling was only 1 g.

As having been described above, the use of the present invention allows us to efficiently obtain high purity cobalt powder and cobalt briquettes. 

1. A method of producing cobalt powder from a cobalt ammine sulfate complex solution derived from a cobalt-containing material, comprising: (1) a seed crystal addition step of adding cobalt powder as seed crystals to the cobalt ammine sulfate complex solution to form a mixed slurry; (2) a reduction step of blowing hydrogen gas into the mixed slurry obtained in the seed crystal addition step to precipitate a cobalt component in the mixed slurry onto the seed crystals by hydrogen reduction reaction to form cobalt powder, and thereby to form a reduced slurry containing the cobalt powder; (3) a growth step of adding the cobalt ammine sulfate complex solution to the cobalt powder obtained by solid-liquid separation of the reduced slurry formed in the reduction step (2) to form a slurry, blowing hydrogen gas into the resulting slurry, and reducing, precipitating, and growing a cobalt component in the slurry on a surface of the cobalt powder by hydrogen reduction reaction to form a grown cobalt powder, and thereby to form a slurry containing the grown cobalt powder; and (4) a recovery step after the reduction step of subjecting the reduced slurry containing the cobalt powder obtained in the reduction step (2) to solid-liquid separation to separate and recover the cobalt powder as a solid phase component, and another recovery step after the growth step of subjecting the slurry containing the cobalt powder obtained in the growth step (3) to solid-liquid separation to separate and recover the cobalt powder as a solid phase component.
 2. The method of producing cobalt powder according to claim 1, wherein, in the seed crystal addition step (1), a dispersant is further added to the mixed slurry when the seed crystals are added to the cobalt ammine sulfate complex solution to form the mixed slurry.
 3. The method of producing cobalt powder according to claim 1, wherein, in the seed crystal addition step (1), an amount of the seed crystals added is 1 to 200% by weight with respect to the weight of cobalt in the cobalt ammine sulfate complex solution.
 4. The method of producing cobalt powder according to claim 1, wherein the cobalt ammine sulfate complex solution is obtained by: a leaching step of dissolving the cobalt-containing material containing nickel and impurities; a nickel separation step of adjusting a pH of the leachate containing cobalt, nickel, and impurities and obtained in the leaching step and then separating the leachate into a crude cobalt sulfate solution and a nickel recovery solution by solvent extraction; a solution purification step of removing the impurities from the crude cobalt sulfate solution obtained in the nickel separation step by any one or a combination of solvent extraction, a sulfurization method, and a neutralization method to obtain a cobalt sulfate solution; and a complexing step of subjecting the cobalt sulfate solution to complexing treatment with ammonia.
 5. The method of producing cobalt powder according to claim 4, wherein the cobalt-containing material is at least one of cobalt and nickel mixed sulfide, crude cobalt sulfate, cobalt oxide, cobalt hydroxide, cobalt carbonate, and metallic cobalt powder.
 6. The method of producing cobalt powder according to claim 4, wherein 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester or di-(2,4,4-trimethylpentyl)phosphinic acid is used as a solvent in the solvent extraction of the solution purification step and the nickel separation step.
 7. The method of producing cobalt powder according to claim 1, wherein, in the seed crystal addition step (1), the cobalt ammine sulfate complex solution has an ammonium sulfate concentration of 100 to 500 g/l, and an ammonium concentration of 1.9 or more by mole with respect to a cobalt concentration in the cobalt ammine sulfate complex solution.
 8. The method of producing cobalt powder according to claim 1, wherein, regarding the hydrogen reduction reaction in the reduction step (2) and the growth step (3), hydrogen reduction is performed by maintaining a temperature of 120 to 250° C. and a pressure of 1.0 to 4.0 MPa.
 9. The method of producing cobalt powder according to claim 2, wherein the dispersant comprises one or more of an acrylate and a sulfonate.
 10. The method of producing cobalt powder according to claim 1, further comprising: a cobalt powder briquetting step of processing the cobalt powder having high purity and obtained in the growth step (3) into cobalt briquettes in a block form using a briquetting machine; and a briquette sintering step of sintering the resulting cobalt briquettes in the block form under a condition of maintaining a temperature of 500 to 1200° C. in a hydrogen atmosphere to form cobalt briquettes as a sintered compact.
 11. The method of producing cobalt powder according to claim 1, further comprising an ammonium sulfate recovery step of concentrating a solution after reaction obtained by separating the cobalt powder as the solid phase component by the solid-liquid separation in the recovery steps (4) after the reduction step (2) and the growth step (3), to precipitate ammonium sulfate to recover ammonium sulfate crystals.
 12. The method of producing cobalt powder according to claim 1, further comprising an ammonia recovery step of adding an alkali to a solution after reaction obtained by separating cobalt powder as the solid phase component by the solid-liquid separation in the recovery steps (4) after the reduction step (2) and the growth step (3), and heating the resulting mixture to volatilize and recover ammonia gas.
 13. The method of producing cobalt powder according to claim 4, wherein the ammonia recovered in the ammonia recovery step is recycled in production processes in the method of producing the cobalt powder, and used as an alkali for pH adjustment in the nickel separation step, as an alkali for neutralization when the neutralization method is used in the solution purification step, and as an alkali used in the complexing step
 4. 14. The method of producing cobalt powder according to claim 4, wherein the seed crystals of the cobalt powder in the seed crystal addition step (1) is cobalt powder formed by adding a reducing agent to the cobalt sulfate solution obtained in the solution purification step
 4. 15. The method of producing cobalt powder according to claim 4, wherein the seed crystals of the cobalt powder in the seed crystal addition step (1) is cobalt powder formed by hydrogen reduction reaction in which an insoluble solid is added to the cobalt ammine sulfate complex solution obtained in the complexing step 4 and hydrogen gas is blown into the resulting mixture at high temperature and high pressure.
 16. Cobalt briquettes obtained using the methods of claim
 1. 